Exemplary embodiments of the present invention relate to a photomask for use in a semiconductor fabrication, and more particularly, to an extreme ultraviolet (EUV) blank mask applicable to extreme ultraviolet lithography (EUVL) and a method of fabricating an EUV mask using the same.
As an integration density of semiconductor devices is increasing in recent years, optical lithography may have a limitation. Small images may be transferred on a wafer by using resolution enhancement technologies, such as an optical proximity correction (OPC), a phase shift mask, an off-axis illumination, and so on. However, as a design rule of semiconductor devices decreases, these technologies may have the limitation. Accordingly, a lithography which can transfer smaller images on a wafer is being developed. An immersion lithography which increases a resolution by using a liquid medium having a higher refractive index than air has recently been proposed. In addition, much research is being conducted on next generation lithography technologies which can ensure finer resolutions.
Examples of next generation lithography technologies include an extreme ultraviolet lithography (EUVL), an electron projection lithography (EPL), a proximity electron-beam lithography (PEL), a proximity X-ray lithography (PXL), and so on. Here, the EUVL is designed to use a wavelength of approximately 13.5 nm. However, a light having the wavelength of approximately 13.5 nm is absorbed by most materials, including air. Thus, the EUVL may use reflective masks and reflective optical systems, instead of transmissive masks and transmissive optical systems.
FIG. 1 is a cross-sectional view schematically illustrating a sectional structure of an blank mask 100 used in a known lithography technology. Referring to FIG. 1, a multilayer reflection layer 120 is disposed over a substrate 110. Although not shown, a backside layer may be disposed under the substrate 110. The multilayer reflection layer 120 may be formed by sequentially stacking materials 121 and 122 having different optical properties. As one example, the multilayer reflection layer 120 may have a structure in which molybdenum (Mo) 121 and silicon (Si) 122 are alternately stacked. A capping layer 130 serving to protect the multilayer reflection layer 120 is disposed over the multilayer reflection layer 120. As one example, the capping layer 130 may include a silicon oxide (SiO2) layer or a silicon (Si) layer. A buffer layer 140 and an absorption layer 150 are sequentially stacked over the capping layer 130. As one example, the buffer layer 140 may include a silicon oxide (SiO2) layer, and the absorption layer 150 may include a tantalum (Ta)-based absorber, such as a tantalum nitride (TaN) layer, or a chromium (Cr)-based absorber.
FIG. 2 is a cross-sectional view schematically illustrating a sectional structure of an mask 102 formed by using the blank mask 100 of FIG. 1. In FIGS. 1 and 2, the same reference numerals refer to the same elements. Referring to FIG. 2, a pattern structure in which a buffer pattern 142 and an absorption pattern 152 are sequentially stacked is disposed over the capping layer 130. In order to fabricate such an mask 102, according to a known art, the absorption pattern 152 and the buffer pattern 142 are formed by patterning the absorption layer (150 in FIG. 1) and the buffer layer (140 in FIG. 1) of the blank mask 100.
However, when the patterning process is performed, specifically, when the patterning process is performed by etching the buffer layer (140 in FIG. 1), the capping layer 130 may be damaged because both of the capping layer 130 and the buffer layer (140 in FIG. 1) are formed of a silicon-based material. The damage of the capping layer 130 may cause defects in the multilayer reflection layer 120. The defects in the multilayer reflection layer 120 may cause a change in the intensity of reflected light. This may serve as a cause of device failure.